Thumbtack press uses a state-of-the-art 8 color archival ink jet process on a heavy bright white stock.
The final print is trimmed to size and protected in an acid-free polyurethane sleeve before shipment in a reinforced box (not an envelope or tube).
In other words: They're stiff, not flimsy. They are fade-resistant past 100 years, and they won't arrive dinged, creased, rolled, or scratched. Just watch this!